1. Field of the Invention
The present invention relates to CPP (current-perpendicular-to-plane) type magnetic sensors or magnetic sensors using the tunnel effect, which are mounted on magnetic reproducing devices, such as a hard disc device, or other magnetic sensing devices. In particular, the present invention relates to a magnetic sensor capable of improving reproducing output and changing rate of resistance, and to a manufacturing method therefor.
2. Description of the Related Art
FIG. 11 is a partial cross-sectional view of a conventional CPP (current-perpendicular-to-plane) type magnetic sensor (spin-valve type thin-film magnetic element) when it is viewed from an opposing face opposing a recording medium.
Reference numeral 1 indicates a first electrode layer, and on this first electrode layer 1, a laminate 9 is provided which is composed of an antiferromagnetic layer 2 formed of a Ptxe2x80x94Mn alloy or the like, a fixed magnetic layer 3 formed of an Nixe2x80x94Fe alloy or the like, a nonmagnetic material layer 4 formed of copper (Cu), and a free magnetic layer 5 formed of an Nixe2x80x94Fe alloy or the like.
As shown in FIG. 11, insulating layers 6 composed of Al2O3 or the like are formed on two sides of the laminate 9 in the track width direction (X direction in the figure) and on the first electrode layer 1, and in addition, a hard bias layer 7 formed of a Coxe2x80x94Pt alloy or the like is formed on each of the insulating layers 6.
In addition, a second electrode layer 8 is formed continuously on the hard bias layers 7 and the free magnetic layer 5.
The magnetization of the fixed magnetic layer 3 is fixed in the height direction (Y direction in the figure) by an exchange coupling magnetic field generated between the fixed magnetic layer 3 and the antiferromagnetic layer 2, and on the other hand, the magnetization of the free magnetic layer 5 is aligned in the track width direction (X direction in the figure) by a longitudinal bias magnetic field from the hard bias layer 7.
In the CPP type magnetic sensor shown in FIG. 11, a sensing current is allowed to flow through each layer forming the laminate 9 in the direction (Z direction in the figure) perpendicular thereto.
Concomitant with the trend toward miniaturization of element size due to increasingly higher recording density in the future, it has been expected that CPP type magnetic sensors in which a sensing current is allowed to flow through individual films in the direction perpendicular thereto more effectively improve reproducing output than CIP (current-in-plane) type magnetic sensors in which a sensing current is allowed to flow through the films in the direction parallel thereto.
In addition, FIG. 23 is a partial cross-sectional view of a conventional magnetic sensor (tunnel type magnetoresistive element) using the tunnel effect when it is viewed from an opposing face opposing a recording medium.
Reference numeral 1 indicates a first electrode layer, and on this first electrode layer 1, a laminate 9 is provided which is composed of an antiferromagnetic layer 2 formed of a Ptxe2x80x94Mn alloy or the like, a fixed magnetic layer 3 formed of a Nixe2x80x94Fe alloy or the like, an insulating-barrier layer 400 formed of Al2O3 or the like, and a free magnetic layer 5 formed of a Nixe2x80x94Fe alloy or the like.
As shown in FIG. 23, insulating layers 6 composed of Al2O3 or the like are formed on two sides of the laminate 9 in the track width direction (X direction in the figure) and on the first electrode layer 1, and in addition, a hard bias layer 7 formed of a Coxe2x80x94Pt alloy or the like is formed on each of the insulating layers 6.
In addition, a second electrode layer 8 is formed continuously on the hard bias layers 7 and the free magnetic layer 5.
The magnetization of the fixed magnetic layer 3 is fixed in the height direction (Y direction in the figure) by an exchange coupling magnetic field generated between the fixed magnetic layer 3 and the antiferromagnetic layer 2, and on the other hand, the magnetization of the free magnetic layer 5 is aligned in the track width direction (X direction in the figure) by a longitudinal bias magnetic field from the hard bias layer 7.
The magnetic sensor shown in FIG. 23 has the structure which is called a tunnel type magnetoresistive element, and the features of this structure are that a layer provided between the fixed magnetic layer 3 and the free magnetic layer 5 is the insulating barrier layer 400, which is an insulating layer, and that the electrode layers 8 and 1 are formed on the top and the bottom of the laminate 9, respectively.
In the tunnel type magnetic sensor shown in FIG. 23 which generates change in resistance using the tunnel effect, when the magnetizations of the fixed magnetic layer 3 and the free magnetic layer 5 are antiparallel to each other, it is most difficult for a tunnel current to flow through the insulating barrier layer 400, so that the resistance becomes a maximum. On the other hand, when the magnetizations of the fixed magnetic layer 3 and the free magnetic layer 5 are parallel to each other, it is most easy for a tunnel current to flow through the insulating layer 400, so that the resistance becomes a minimum.
By using this principle, when the magnetization of the free magnetic layer 5 varies by the influence of an external magnetic field, change in electrical resistance is detected as change in voltage, thereby sensing a leakage magnetic field from the recording medium.
However, in a magnetic sensor having the structure shown in FIG. 11 or 23, problems described below have occurred.
Concomitant with the trend toward higher recording density in the future, when the track width Tw which is defined by the width dimension in the track width direction of the upper surface of the free magnetic layer 5 is decreased, the size of the free magnetic layer 5 itself is decreased, and hence, even when a longitudinal bias magnetic field is supplied from the hard bias layer 7 to the free magnetic layer 5, the free magnetic layer 5 is difficult to be appropriately placed in a single domain state in the track width direction (X direction in the figure). In addition, since the influence of a demagnetizing field of the free magnetic layer 5 is enhanced, the stability of reproducing properties is degraded.
In order to solve the problems described above, a method in which the film thickness of the hard bias layer 7 is increased so as to supply an intense longitudinal bias magnetic field to the free magnetic layer 5 may be considered; however, in the method described above, since the magnetization of the free magnetic layer 5 formed in a very small area tends to be fixed, and the magnetization change cannot be performed sensitively in response to an external magnetic field, a problem of degradation of reproducing output may arise in some cases.
Next, as shown in FIG. 23, the insulating layers 6 are provided on two sides of the laminate 9 in the track width direction. The insulating layers 6 are provided so that a current flowing from the electrode layer 1 or 8 through the laminate 9 flows effectively.
However, since the hard bias layer 7 is formed on the insulating layer 7, a part of the current flowing from the electrode layer 1 or 8 through the laminate 9 is shunted to the hard bias layer 7. The current thus shunted flows into the insulating barrier layer 400, the fixed magnetic layer 3, or the like not through the free magnetic layer 5.
That is, in addition to a regular route through which a current flows from the electrode layer 1 or 8 in the laminate 9, an additional current route through which a part of the current is shunted to the hard bias layer 7 not through the free magnetic layer 5 is formed, resulting in shut loss. Accordingly, decrease in changing rate of resistance (xcex94R/R) occurs.
In order to solve the problems described above, as shown in FIG. 24 (a partial cross-sectional view showing an enlarged portion in FIG. 23), by forming the insulating layers 6 having a large thickness on two side surfaces 5a of the free magnetic layer 5, two side surfaces of the laminate 9 are properly covered with the insulating layers 6, and the amount of current shunted from the electrode layer 1 or 8 to the hard bias layer 7 can be decreased; however, when the thick insulating layer 6 is provided between the free magnetic layer 5 and the hard bias layer 7, the longitudinal bias magnetic field, which is to be supplied to the free magnetic layer 5 from the hard bias layer 7, is decreased, and as a result, since the free magnetic layer 5 cannot be placed in a single domain state, degradation of reproducing properties occurs.
In addition, as described above, in the magnetic sensor having the structure shown in FIG. 23, when the track width Tw is decreased with increase in recording density in the future, the surface area of the laminate 9 in the direction parallel to the film surface thereof (the surface formed by the X and Y axes) is decreased, and DC resistance (DCR) is extremely increased, resulting in degradation of reproducing characteristics such as reproducing output.
Accordingly, the present invention was made to solve the problems described above, and an object of the present invention is to provide a magnetic sensor, in which reproducing properties such as reproducing output or changing rate of resistance can be appropriately improved so as to meet the requirements of higher recording density in the future by properly improving a bias method for aligning the magnetization of a free magnetic layer and the structure thereof, and to provided a manufacturing method therefor.
A magnetic sensor of the present invention comprises a laminate having a first antiferromagnetic layer, a fixed magnetic layer formed on the upper surface of the first antiferromagnetic layer, the magnetization of the fixed magnetic layer being fixed in a predetermined direction by an exchange coupling magnetic field generated between the first antiferromagnetic layer and the fixed magnetic layer, and a nonmagnetic material layer formed on the upper surface of the fixed magnetic layer; insulating layers formed on two sides in the track width direction of the laminate; a free magnetic layer formed continuously on the upper surface of the nonmagnetic material layer and the upper surfaces of the insulating layers, the magnetization of the free magnetic layer being aligned in the direction crossing that of the fixed magnetic layer; a second antiferromagnetic layer formed at the upper side of the free magnetic layer; a recess portion formed in the second antiferromagnetic layer from the surface thereof in the direction toward the laminate at the position opposing the laminate in the thickness direction; and electrode layers formed at the lower side of the laminate and at the upper side of the second antiferromagnetic layer.
The present invention relates to a CPP (current-perpendicular-to-plane) type magnetic sensor, and a sense current flows in the direction perpendicular to the film surfaces of individual layers forming the magnetic sensor.
In the present invention, a conventional hard bias method in which hard bias layers are provided on two sides in the track width direction of the free magnetic layer is not employed, and an exchange bias method in which the second antiferromagnetic layer is provided at the upper side of the free magnetic layer is employed.
When the exchange bias method is employed, the width dimension in the track width direction of the free magnetic layer can be formed to be larger than the track width Tw.
In particular, according to the present invention, the free magnetic layer can be formed not only on the laminate, but also on the insulating layers formed at the two sides of the laminate.
Accordingly, even when the track width Tw is decreased concomitant with the trend toward higher recording density in the future, regardless of the dimensions of the track width Tw and the width dimension of the laminate, the width dimension of the free magnetic layer can be formed large. Hence, the free magnetic layer can be appropriately placed in a single domain state, the influence of the demagnetizing field of the free magnetic layer can be decreased, and as a result, a magnetic sensor which has superior sensitivity and which can appropriately improve reproducing output can be manufactured even when the track width Tw is decreased in the future.
Next, in the present invention, the laminate having the antiferromagnetic layer, the fixed magnetic layer, and the nonmagnetic material layer is covered with the insulating layers at two side surfaces in the track width direction of the laminate.
Previously, since the hard bias layers are provided on the two sides of the free magnetic layer, and current shunted to these hard bias layers flows through the nonmagnetic material layer and the fixed magnetic layer but the free magnetic layer, shunt loss occurs, thereby degrading changing rate of resistance. However, in the present invention, since no hard bias layers are provided, and the two sides of the laminate are covered with the insulating layers, a current from the electrode layer appropriately flows through the free magnetic layer and then the laminate, and as a result, compared the convention structure described above, shut loss can be decreased and changing rate of resistance can be improved.
In addition, in the present invention, the width dimension in the track width direction of the upper surface of the laminate is preferably equal to or smaller than the width dimension in the track width direction of the bottom surface of the recess portion.
The width dimension in the track width direction of the upper surface of the laminate is defined as an electric track width. Accordingly, in order to increase DC resistance (DCR), the width dimension of the laminate described above is preferably decreased as small as possible.
On the other hand, the width dimension in the track width direction of the bottom surface of the recess portion is defined as a magnetic track width Tw. That is, a part of the free magnetic layer, which is located at the position opposing the recess portion, substantially serves as a sensing region of the magnetoresistive effect.
Accordingly, the sensing region of the free magnetic layer is decreased with decrease in the dimension in the track width direction of the bottom surface of the recess portion; however, when the sensing region is too much decreased, it is not preferable since the reproducing output is decreased.
That is, in order to fulfill the requirements of higher recording density appropriately, the sensing region described above (magnetic track width Tw) must be decreased; however, when it is too much decreased, the reproducing output is also decreased. On the other hand, in order to increase DC resistance, the electric track width defined by the width dimension of the upper surface of the laminate is preferably further decreased regardless of the dimension of the magnetic track width Tw.
Consequently, in the present invention, the width dimension in the track width direction of the upper surface of the laminate is formed to be equal to or smaller than the width dimension in the track width direction of the bottom surface of the recess portion. As a result, the DC resistance (DCR) and the reproducing output of a CPP type magnetic sensor can be appropriately improved.
In the nonmagnetic material layer according to the present invention, element Ru, Rh, Re, Os, Ir, Pt, Pd, or the mixture thereof is preferably present at a high concentration at the upper surface side of the nonmagnetic material layer as compared to that at the lower surface side thereof.
In the present invention, the nonmagnetic material layer is preferably composed of a lower layer, which is formed of a Cu layer, an Rh layer, an Ru layer, an Re layer, an Os layer, a Cr layer, an Ir layer, a Pt layer, a Pd layer, or a layer containing at least two elements forming the above-mentioned layers, and an upper layer which is provided on the lower layer and which is formed of an Ru layer, an Rh layer, an Re layer, an Os layer, an Ir layer, a Pt layer, a Pd layer, or a layer containing at least two elements forming the above layers.
In the present invention, the entire nonmagnetic material layer may also be formed of an Ru layer, an Rh layer, an Re layer, an Os layer, an Ir layer, a Pt layer, a Pd layer, or a layer containing at least two elements forming the above layers.
In addition, the magnetic sensor of the present invention may further comprise a nonmagnetic interlayer and a ferromagnetic layer on the free magnetic layer in that order, and the second antiferromagnetic layer is preferably formed on the ferromagnetic layer.
In the present invention, the three layers, that is, the free magnetic layer, the nonmagnetic interlayer, and the ferromagnetic layer, form a laminated ferrimagnetic structure. The ferromagnetic layer is magnetized in the track width direction by an exchange coupling magnetic field generated between the ferromagnetic layer and the second antiferromagnetic layer provided on the two sides in the track width direction of the recess portion formed therein.
On the other hand, the free magnetic layer described above is magnetized antiparallel to the magnetization direction of the ferromagnetic layer by a coupling magnetic field generated between the ferromagnetic layer and the free magnetic layer due to the RKKY interaction.
In the present invention, since the magnetizations of parts of the free magnetic layer and the ferromagnetic layer, which are formed under the second antiferromagnetic layer at the two sides in the track width direction of the recess portion formed therein, are fixed, regions corresponding to the parts described above are regions having no relation with the magnetoresistive effect.
On the other hand, since parts of the ferromagnetic layer and the free magnetic layer, which are formed under the recess portion, are placed in a weak single domain state so that the magnetizations thereof may be inverted in response to an external magnetic field, a region corresponding to the parts described above serves substantially as a sensing region of the magnetoresistive effect.
As described above, when a laminated ferrimagnetic structure is formed of the free magnetic layer, the nonmagnetic interlayer free, and the ferromagnetic layer laminated to each other in that order from the bottom, the single domain structure in which the magnetization of the free magnetic layer is stabilized can be formed, and hence the reproducing output can be appropriately improved.
According to the present invention, the recess portion may be formed to extend to the surface of the ferromagnetic layer so that the surface thereof is exposed at the bottom of the recess portion or may be formed to extend to the surface of the nonmagnetic interlayer so that the surface thereof is exposed at the bottom of the recess portion.
According to the present invention, a method for manufacturing a magnetic sensor comprises a step (a) of forming a laminate composed of a first antiferromagnetic layer, a fixed magnetic layer, and a nonmagnetic material layer provided in that order on a first electrode layer; a step (b) of forming a lift-off resist layer on the upper surface of the laminate and removing two side surfaces thereof, which are not covered with the resist layer, in the track width direction; a step (c) of forming insulating layers on two sides in the track width direction of the laminate and removing the resist layer: a step (d) of forming a free magnetic layer continuously on the insulating layers and the nonmagnetic material layer and forming a second antiferromagnetic layer on the free magnetic layer; a step (f) of forming a mask layer having an opening at the position opposing the laminate in the thickness direction on the second antiferromagnetic layer and excavating the second antiferromagnetic layer which is exposed in the opening to form a recess portion in the second antiferromagnetic layer; and a step (g) of forming a second electrode layer on the second antiferromagnetic layer.
In the manufacturing method described above, in accordance with an exchange bias method in which the second antiferromagnetic layer is formed at the upper side of the free magnetic layer, the free magnetic layer can be placed in a single domain state in the track width direction.
According to the method described above, compared to the case in which the magnetization is performed by a hard bias method, the free magnetic layer can be formed to extend long in the track width direction, and in addition, the free magnetic layer can also be formed on the insulating layers provided on the two sides of the laminate. Consequently, the free magnetic layer can be formed to be large regardless of the track width Tw and the dimensions of the laminate, and hence, even when element sizes are decreased concomitant with the trend toward higher recording density in the future, the free magnetic layer can be appropriately placed in a single domain state by an exchange coupling magnetic field generated between the second antiferromagnetic layer and the free magnetic layer.
In addition, since the two sides of the laminate, which is composed of the first antiferromagnetic layer, the fixed magnetic layer, and the nonmagnetic material layer and which is provided below the free magnetic layer, can be approximately covered with the insulating layers, a magnetic sensor in which shunt loss is unlikely to occur and changing rate of resistance can be appropriately improved can be manufactured.
According to the method of the present invention for manufacturing the magnetic sensor, a magnetic sensor capable of appropriately improving reproducing properties such as reproducing output or changing rate of resistance can be easily manufactured even when recording density is increased.
In addition, in the step (f) described above of the present invention, the width dimension in the track width direction of the bottom surface of the recess portion is preferably formed to be larger than the width dimension in the track width direction of the laminate.
In the step (a) of the present invention, the nonmagnetic material layer is preferably composed of a lower layer, which is formed of a Cu layer, an Rh layer, an Ru layer, an Re layer, an Os layer, a Cr layer, an Ir layer, a Pt layer, a Pd layer, or a layer containing at least two elements forming the above-mentioned layers, and an upper layer which is provided on the lower layer and which is formed of an Ru layer, an Rh layer, an Re layer, an Os layer, an Ir layer, a Pt layer, a Pd layer, or a layer containing at least two elements forming the above layers.
When a nonmagnetic material layer formed of Cu or the like is exposed to the air, a problem in which bulk scattering cannot be fully obtained due to oxidation or damages caused by contamination may arise in some cases, and as a result, degradation of output properties such as changing rate of resistance is likely to occur.
Accordingly, in the present invention, after the lower layer composed of Cu described above is formed, the upper layer such as an Ru layer is sequentially formed on the lower layer, so that the lower layer is appropriately prevented from being exposed to the air. When being exposed to the air, since the upper layer such as an Ru layer is not significantly degraded by contamination and is not liable to oxidize, the lower layer composed of Cu or the like can be appropriately protected from degradation caused by exposure to the air, and since the lower layer and the upper layer can be formed from a nonmagnetic material, the upper layer and the lower layer can form a nonmagnetic material layer.
In the step (a) of the present invention, the nonmagnetic material layer may be formed of an Ru layer, an Rh layer, an Re layer, an Os layer, an Ir layer, a Pt layer, a Pd layer, or a layer containing at least two elements forming the above layers.
In the step (d) of the present invention, it is preferable that after a nonmagnetic interlayer and a ferromagnetic layer are formed in that order on the free magnetic layer, the second antiferromagnetic layer be formed on the ferromagnetic layer.
In the step (f) of the present invention, the second antiferromagnetic layer may be excavated to expose the surface of the ferromagnetic layer, or a part of the second antiferromagnetic layer may be excavated. In this step, the part of the second antiferromagnetic layer remaining under the recess portion is a thin-film so that the antiferromagnetic functions may be degraded to some extent. Consequently, an exchange coupling magnetic field between the region under the recess portion and the free magnetic layer (or the ferromagnetic layer) may not be generated, or only a very weak exchange coupling magnetic field is generated, and hence, the magnetization of the free magnetic layer (or the ferromagnetic layer) cannot be firmly fixed.
Accordingly, a part of the free magnetic layer (and a part of the ferromagnetic layer) located under the recess portion formed in the second antiferromagnetic layer can be used as a sensing region in which the magnetoresistive effect can be appropriately obtained.
According to the present invention, the mask layer is preferably formed from an inorganic material.
In addition, instead of the steps (d) to (g) described above, the present invention may further comprises a step (h) of, after the free magnetic layer is formed continuously on the insulating layers and the nonmagnetic material layer, forming a nonmagnetic interlayer on the free magnetic layer; a step (i) of forming a lift-off resist layer on the nonmagnetic interlayer at the position opposing the laminate in the thickness direction, and forming a ferromagnetic layer and a second antiferromagnetic layer in that order on each of two sides in the track width direction of the nonmagnetic interlayer, which are not covered with the resist layer, so that the width dimension in the track width direction of a part of the nonmagnetic interlayer exposed between the second antiferromagnetic layers is smaller than the width dimension in the track width direction of the upper surface of the laminate; and a step (j) of removing the resist layer.
When the steps (i) and (j) are used, excavation of the second ferromagnetic layer in the step (f) is not necessary. In addition, by the steps (i) and (j), the upper surface of the nonmagnetic interlayer can be exposed at the bottom of the recess portion formed between the second antiferromagnetic layers.
According to the present invention, a magnetic sensor comprises a laminate formed of a first antiferromagnetic layer, a fixed magnetic layer formed on the upper surface of the first antiferromagnetic layer, the magnetization of the fixed magnetic layer being fixed in a predetermined direction by an exchange coupling magnetic field generated between the first antiferromagnetic layer and the fixed magnetic layer, and a spacer layer which is formed on the upper surface of the fixed magnetic layer and which contains at least an insulating barrier layer; insulating layers formed on two sides in the track width direction of the laminate; a free magnetic layer formed continuously on the spacer layer and the insulating layers, the magnetization of the free magnetic layer being aligned in the direction crossing that of the fixed magnetic layer; a second antiferromagnetic layer formed at the upper side of the free magnetic layer; a recess portion formed in the second antiferromagnetic layer from the surface thereof in the direction toward the laminate at the position opposing to the laminate in the thickness direction, the width dimension in the track width direction of the bottom surface of the recess portion being formed to be smaller than the width dimension in the track width direction of the upper surface of the laminate; and electrode layers formed at the lower side of the laminate and at the upper side of the second antiferromagnetic layer.
In the present invention, a conventional hard bias method in which hard bias layers are provided on two sides in the track width direction of a free magnetic layer is not used, and an exchange bias method in which a second antiferromagnetic layer is provided at the upper side of the free magnetic layer is employed.
When the exchange bias method is employed, the width dimension in the track width direction of the free magnetic layer can be formed to be larger than the track width Tw.
In particular, the free magnetic layer can be formed not only on the laminate but also on the insulating layers formed on the two sides of the laminate.
Consequently, even when the track width Tw is decreased concomitant with the trend toward higher recording density in the future, regardless of the dimension of the track width Tw, the width dimension of the free magnetic layer can be formed to be large. Accordingly, since the free magnetic layer can be appropriately placed in a single domain state, and the influence of the demagnetizing field of the free magnetic layer can be weakened, even when the track width Tw is decreased in the future, a magnetic sensor which has superior sensitivity and which can appropriately improve reproducing output can be manufactured.
Next, in the present invention, the two sides in the track width direction of the laminate formed of the antiferromagnetic layer, the fixed magnetic layer, and the spacer layer are covered with the insulating layers.
Previously, since hard bias layers are provided on two sides of the free magnetic layer, and current shunted to these hard bias layers flows through the insulating barrier layer and the fixed magnetic layer but the free magnetic layer, shunt loss occurs, thereby degrading changing rate of resistance. However, in the present invention, since no hard bias layers are provided, and the two sides of the laminate are covered with the insulating layers, a current from the electrode layer appropriately flows through the free magnetic layer and then the laminate, and as a result, compared the convention structure described above, shunt loss can be reduced and changing rate of resistance can be improved.
Next, in the present invention, the width dimension in the track width direction of the upper surface of the laminate is formed to be larger than the width dimension (track width Tw) in the track width direction of the bottom surface of the recess portion.
That is, in the present invention, since a surface area parallel to the film surface of the laminate can be formed to be large regardless of the dimension of the track width Tw, DC resistance (DCR) can be appropriately decreased as compared to the conventional structure described above, and hence, reproducing properties such as reproducing output can be improved.
In the present invention, the insulating barrier layer is preferably formed of Alxe2x80x94O, Sixe2x80x94O, or Alxe2x80x94Sixe2x80x94O.
In addition, according to the present invention, the spacer layer preferably has a laminated structure composed of the insulating barrier layer and a protective layer which is provided thereon and which contains at least one selected from the group consisting of Ru, Ir, Rh, Os, Re, Pt, and Pd.
In the present invention, it is preferable that a nonmagnetic interlayer and a ferromagnetic layer be formed in that order on the free magnetic layer and that the second antiferromagnetic layer be formed on the ferromagnetic layer.
According to the present invention, the three layers, that is, the free magnetic layer, the nonmagnetic interlayer, and the ferromagnetic layer, form a laminated ferrimagnetic structure. The ferromagnetic layer is magnetized in the track width direction by an exchange coupling magnetic field generated between the ferromagnetic layer and the second antiferromagnetic layer provided on the two sides of the recess.
On the other hand, the free magnetic layer is magnetized antiparallel to the magnetization direction of the ferromagnetic layer by a coupling magnetic field generated between the ferromagnetic layer and the free magnetic layer due to the RKKY interaction.
In the present invention, the magnetizations of parts of the ferromagnetic layer and the free magnetic layer, which are formed under the second antiferromagnetic layer at the two sides in the track width direction of the recess portion, are fixed, and regions corresponding to the parts described above are regions having no relation with the magnetoresistive effect.
On the other hand, parts of the ferromagnetic layer and the free magnetic layer, which are formed under the recess portion are placed in a weak single domain state so that the magnetizations thereof may be inverted in response to an external magnetic field, and hence a region corresponding to the parts described above serves substantially as a sensing region of the magnetoresistive effect.
As described above, when a ferrimagnetic structure composed of the nonmagnetic interlayer and the ferromagnetic layer provided in that order on the free magnetic layer is formed, a single domain structure in which the magnetization of the free magnetic layer is stabilized can be formed, and hence reproducing output can be appropriately improved.
According to the present invention, the recess portion described above may be formed to extend to the surface of the ferromagnetic layer so that the surface thereof is exposed at the bottom of the recess portion or may be formed to extend to the surface of the nonmagnetic interlayer so that the surface thereof is exposed at the bottom of the recess portion.
A method of the present invention for manufacturing a magnetic sensor comprises a step (a) of forming a laminate composed of a first antiferromagnetic layer, a fixed magnetic layer, and an insulating barrier layer in that order on a first electrode layer; a step (b) of forming a lift-off resist layer on the upper surface of the laminate and removing two side surfaces, which are not covered with the resist layer, in the track width direction of the laminate; a step (c) of forming insulating layers on two sides in the track width direction of the laminate and removing the resist layer: a step (d) of forming a free magnetic layer continuously on the insulating layers and the insulating barrier layer and forming a second antiferromagnetic layer on the free magnetic layer; a step (f) of forming a mask layer having an opening at the position opposing the laminate in the thickness direction on the second antiferromagnetic layer and excavating the second antiferromagnetic layer which is exposed in the opening to form a recess portion in the second antiferromagnetic layer so that the width dimension in the track width direction of the bottom surface of the recess portion is smaller than the width dimension in the track width direction of the upper surface of the laminate; and a step (g) of forming a second electrode layer on the second antiferromagnetic layer.
According to the manufacturing method described above, since the exchange bias method in which the second antiferromagnetic layer is formed at the upper side of the free magnetic layer is employed, the free magnetic layer can be placed in a single domain state in the track width direction.
According to the method described above, compared to the case in which the magnetization is performed by a hard bias method, the free magnetic layer can be formed to extend long in the track width direction and can be appropriately placed in a single domain state by an exchange coupling, magnetic field generated between the second antiferromagnetic layer and the free magnetic layer.
In addition, since the laminate composed of the first antiferromagnetic layer, the fixed magnetic layer, and the insulating barrier layer formed under the free magnetic layer is appropriately covered with the insulating layers at the two sides in the track width direction of the laminate, shunt loss is not likely to occur, and hence a magnetic sensor capable of appropriately improving changing rate of resistance can be manufactured.
The track width Tw can be controlled by the width dimension in the track width direction of the bottom surface of the recess portion formed in the second antiferromagnetic layer, and even when the track width is decreased, the width dimension in the track width direction of the laminate can be formed to be large regardless of the dimension of the track width Tw. Accordingly, DC resistance (DCR) of the laminate can be appropriately increased, and a magnetic sensor capable of increasing reproducing output can be easily formed as compared to that in the past.
Consequently, according to the method for manufacturing a magnetic sensor of the present invention, even when recording density is increased, a magnetic sensor capable of appropriately improving reproducing properties such as reproducing output or changing rate of resistance can be easily manufactured.
In the step (a) of the present invention, the insulating barrier layer preferably comprises an insulating material composed of Alxe2x80x94O, Sixe2x80x94O, or Alxe2x80x94Sixe2x80x94O.
In addition, in the step (a) of the present invention, it is preferable that after a layer composed of Al, Si, or Alxe2x80x94Si is formed on the fixed magnetic layer, the layer described above be oxidized to form an insulating barrier layer composed of Alxe2x80x94O, Sixe2x80x94O, or Alxe2x80x94Sixe2x80x94O. As the oxidation method therefor, for example, there may be mentioned natural oxidation, plasma oxidation, radical oxidation, ion-assist-oxidation (IAO), or CVD oxidation.
In addition, in the step (a) of the present invention, a protective layer composed of at least one selected from the group consisting of Ru, Ir, Rh, Os, Re, Pt, and Pd is preferably formed on the insulating barrier layer, whereby the protective layer and the insulating barrier layer form a spacer layer.
When the insulating barrier layer formed of the Alxe2x80x94O or the like mentioned above is exposed to the air, barrier properties are degraded due to damages caused by contamination or the like, and as a result, degradation of reproducing properties such as changing rate of resistance is likely to occur.
Accordingly, in the present invention, after the insulating barrier layer composed of the Alxe2x80x94O or the like mentioned above is formed, a protective layer is sequentially formed from Ru or the like on the insulating barrier layer, thereby appropriately preventing the insulating barrier layer from being exposed to the air. Consequently, although the laminate having the protective layer provided on the insulating barrier layer is exposed to the air, the barrier properties of the insulating barrier layer can be appropriately maintained.
In the step (d) of the present invention, it is preferable that after a nonmagnetic interlayer and a ferromagnetic layer are formed on the free magnetic layer in that order, the second antiferromagnetic layer be formed on the ferromagnetic layer.
In the step (f) of the present invention, the second antiferromagnetic layer may be excavated to expose the surface of the ferromagnetic layer, or a part of the second antiferromagnetic layer may be excavated. In this step, the part of the second antiferromagnetic layer remaining under the recess portion is a thin-film so that antiferromagnetic functions may be degraded to some extent. Consequently, an exchange coupling magnetic field between the region under the recess portion and the free magnetic layer (or the ferromagnetic layer) may not be generated, or only a very weak exchange coupling magnetic field may be generated, and hence, the magnetization of the free magnetic layer (or the ferromagnetic layer) cannot be firmly fixed.
Accordingly, the free magnetic layer (and the ferromagnetic layer) under the recess portion formed in the second antiferromagnetic layer can be used as a sensing region in which the magnetoresistive effect can be appropriately obtained.
In the present invention, the mask layer is preferably formed from an inorganic material.
In addition, instead of the steps (d) to (g), the present invention may further comprises a step (h) of, after the free magnetic layer is formed continuously on the insulating layers and the insulating barrier layer, forming a nonmagnetic interlayer on the free magnetic layer; a step (i) of forming a lift-off resist layer on the nonmagnetic interlayer at the position opposing the laminate in the thickness direction, and forming ferromagnetic layers and second antiferromagnetic layers in that order on two sides, which are not covered with the resist layer, in the track width direction of the nonmagnetic interlayer so that the width dimension in the track width direction of the surface of the nonmagnetic interlayer which is exposed between the second antiferromagnetic layers is smaller than the width dimension in the track width direction of the upper surface of the laminate; and a step (j) of removing the resist layer.
When the steps (i) and (j) are used, excavation of the second ferromagnetic layer in the step (f) is not necessary. In addition, by the steps (i) and (j), the upper surface of the nonmagnetic interlayer can be exposed at the bottom of the recess portion formed between the second antiferromagnetic layer.